The present invention relates to a magnetron sputtering apparatus, more particularly, to a magnetron sputtering apparatus capable of improving the magnetic field on the surface of a target to form a metal film without any deffect such as crack or the like.
As a method for forming a useful metal film on the surface of various substrates, there have been broadly employed methods such as vacuum depositing, plating, sputtering or others.
Among these, the vacuum depositing has the disadvantage that it is difficult to control the composition of a film made of a multi-component alloy which contains elements different from one another in vapor pressure. Plating causes a problem with respect to environmental pollution which may take place in treating the waste liquor. Therefore, attention has been directed to sputtering. For example, for the preparation of vertical type magnetic recording media having magnetic recording films of cobalt (Co)-chromium (Cr) alloy, there have been manufactured currently on the sputtering rather than the vacuum depositing since there is a large difference in vapor pressure between Co and Cr.
In the prior art film forming apparatus which utilizes the sputtering process, there is normally used a planar diode sputtering apparatus of such a type that two electrodes are used one for each of the target and substrate to form an electric field. However, the prior art apparatus provides a formation of film at a reduced speed. In addition, the temperature of the substrate increases up to several hundreds of degrees centigrade. It becomes, therefore, difficult to form a sputter film on a substrate made of a polymer since the substrate itself is deformed by heat.
In order to overcome such a disadvantage in the prior art sputtering apparatus, a magnetron sputtering apparatus has been developed in which films can be formed more rapidly without any rise of temperature in substrates. The developed apparatus comprises electrodes and magnetic poles which are arranged such that the electric field intersects the magnetic field in a sputter chamber in so that they are perpendicular to each other, as shown in FIG. 1. In this figure, A is a magnet system while B is an exhaust system. In this magnetron sputtering apparatus, for instance, as shown in FIG. 13, the magnetic field on an imaginary perpendicular line passing to a target through or by the magnetic symmetry axis is entirely directed to either the target or substrate.
However, according to said apparatus, defects with respect to structure such as micro-crack, crack and others often happens on the surface of the formed films. Among these defects, the crack is serious in that it increases as films are increased in thickness and that cracks remarkably appear on films where substrates are made of a polymer subject to heat-deformation, such as acrylonitrile-butadiene-styrene resin. Cracks are undesirable, particularly, if films are formed for various purposes such as magnetic recording, decoration, resist, surface hardening and others. Cracks, for example, generated on the magnetic recording layer of a magnetic recording medium lead to troubles, that is, (1) reduction of recording signals; (2) frictional wear of the magnetic head according to sliding at a time of recording or playback; and (3) the reduced durability of the magnetic recording medium itself. In addition, where a vertical type magnetic recording medium is formed with a magnetic recording layer of ferromagnetic Co-Cr alloy film, etc. by the use of the prior art magnetron sputtering apparatus, a new and important problem is caused in that the coercive force perpendicular to the surface of the magnetic recording film is reduced to decrease the output on reproducing.
In order to overcome such a disadvantage, it is effective to increase the substrate in temperature even in a magnetron sputtering apparatus. Such a procedure, however, cannot be applied to polymers subject to heat-deformation as in the planar diode sputtering apparatus, and also does not provide a desired means for preventing any crack since the magnetron sputtering apparatus constructed according to this principle becomes more complicated.